Broaden accepted values in non-urlencoded headers

After open-telemetry#4103 we accept non url-encoded headers for OTLP. Naively this
implementation only accepts digits, ascii letters, underscores (\w) and spaces.
Instead broaden the accepted chars to what we accept for urlencoded
values so that we accepts = to allow for base64 encoded values.

Author: xrmx

opentelemetry-api/src/opentelemetry/util/re.py

@@ -32,12 +32,14 @@
 # A value contains a URL-encoded UTF-8 string. The encoded form can contain any
 # printable US-ASCII characters (0x20-0x7f) other than SP, DEL, and ",;/
 _VALUE_FORMAT = r"[\x21\x23-\x2b\x2d-\x3a\x3c-\x5b\x5d-\x7e]*"
+# Like above with SP included
+_LIBERAL_VALUE_FORMAT = r"[\x20\x21\x23-\x2b\x2d-\x3a\x3c-\x5b\x5d-\x7e]*"
 # A key-value is key=value, with optional whitespace surrounding key and value
 _KEY_VALUE_FORMAT = rf"{_OWS}{_KEY_FORMAT}{_OWS}={_OWS}{_VALUE_FORMAT}{_OWS}"
 
 _HEADER_PATTERN = compile(_KEY_VALUE_FORMAT)
 _LIBERAL_HEADER_PATTERN = compile(
-    rf"{_OWS}{_KEY_FORMAT}{_OWS}={_OWS}[\w ]*{_OWS}"
+    rf"{_OWS}{_KEY_FORMAT}{_OWS}={_OWS}{_LIBERAL_VALUE_FORMAT}{_OWS}"
 )
 _DELIMITER_PATTERN = compile(r"[ \t]*,[ \t]*")
 

opentelemetry-api/tests/util/test_re.py

@@ -89,6 +89,11 @@ def test_parse_env_headers_liberal(self):
         inp = self._common_test_cases() + [
             # valid header value
             ("key=value othervalue", [("key", "value othervalue")], False),
+            (
+                "key=value Other_Value==",
+                [("key", "value Other_Value==")],
+                False,
+            ),
         ]
         for case_ in inp:
             headers, expected, warn = case_